JP2004251183A - Control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a control device for an internal combustion engine capable of easily and appropriately performing the engine control based on the operating condition of a variable valve mechanism and a change of the internal EGR quantity. <P>SOLUTION: This engine controlling electronic control device used for an internal combustion engine provided with a variable valve mechanism corrects the ignition timing in response to a change of the internal EGR quantity following operation of the variable valve mechanism. When correcting the ignition timing, VVT correction quantity AVVT of the ignition time is computed by multiplying a ratio between a square numeral of the real valve overlap quantity realOL and a square numeral of the target valve overlap quantity tOL and a base correction quantity AVVTb, which is obtained on the basis of the engine speed NE and the engine load ratio KL. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

（残留既燃ガス量Ｍｅｇｒ１の算出）
残留既燃ガス量Ｍｅｇｒ１は、式（２）に示されるような吸気弁開直前のシリンダ内の状態に基づく気体状態方程式で表すことができる。ここでＰｍ：吸気管圧力、Ｐｅ：排気管圧力、Ｒｅ：既燃ガスの気体定数、Ｔｅ：排気温度、Ｖ：吸気弁開直前のシリンダ容積をそれぞれ示している。
【００３７】
【数２】

更に吸気弁開直前のシリンダ容積Ｖは、吸気弁開時期Ｔｏｐｅｎ（ＢＴＤＣ）、シリンダボア径ｒｂ、ピストンのストロークＳ、ピストンが上死点にあるときの燃焼室の容積、すなわちクリアランス容積Ｖｃに基づき、式（３）にて求められる。
【００３８】
【数３】

上式（３）においてシリンダボア径ｒｂ、ストロークＳ、及びクリアランス容積Ｖｃは、設計諸元等により決まる定数である。そのため、吸排気弁のバルブタイミングを可変とする可変動弁機構を備える内燃機関の場合、シリンダ容積Ｖは、吸気弁開時期Ｔｏｐｅｎの関数ｆ_２（Ｔｏｐｅｎ）として求めることができる。
【００３９】
（吹返し既燃ガス量Ｍｅｇｒ２の算出）
バルブオーバーラップ期間には、排気管圧力Ｐｅと吸気管圧力Ｐｍとの差圧により、排気管から吸気管に向けて既燃ガスが流れ、シリンダ内に排気管の既燃ガスが吹き返されるようになる。このときの既燃ガスの流通経路では、吸排気弁の開口は、流路面積の局所的に狭められた絞りとなっている。したがって、このときの既燃ガスの流れの様相は、図４のようなモデルで表すことができ、その流量Ｑは、絞りの流量算出式を用いて求めることができる。
【００４０】
ここでは、そうした絞りの流量算出式として、式（４）を用いている。ここで、κ：既燃ガスの比熱比、μ：流量係数、Ａ：バルブ開口面積をそれぞれ示している。
【００４１】
【数４】

上式（４）のΦ（Ｐｍ／Ｐｅ）は、１／（κ＋１）＜Ｐｍ／Ｐｅのとき、式（５）で表される。
【００４２】
【数５】

一方、１／（κ＋１）≧Ｐｍ／Ｐｅのときには、上式（４）のΦ（Ｐｍ／Ｐｅ）は式（６）で表される。
【００４３】
【数６】

よって、排気の吹返しによりシリンダ内に導入される既燃ガスの量、すなわち吹返し既燃ガス量Ｍｅｇｒ２は、そうした絞りの既燃ガス流量のバルブオーバーラップ期間における時間積分値として求めることができる。更に吸気管圧力Ｐｍ、排気管圧力Ｐｅ、排気温度Ｔｅ、及び既燃ガスの比熱比κは、急激に変化することはないため、バルブオーバーラップ中のそれらの値は一定と見なすことができる。そのため、吹返し既燃ガス量Ｍｅｇｒ２は、有効バルブ開口面積μＡ（＝流量係数μ×バルブ開口面積Ａ）の時間積分値Σ（μＡ）に比例する値として求めることができる。よって吹返し既燃ガス量Ｍｅｇｒ２は、式（７）で表すことができる。
【００４４】
【数７】

（有効バルブ開口面積の時間積分値Σ（μＡ）の算出）
バルブオーバーラップ期間の排気の吹返しに際して、図５−Ａに示すように、吸気弁の有効バルブ開口面積μｉ Ａｉ が排気弁の有効バルブ開口面積μｅ Ａｅよりも小さいときには、吸気弁が絞りとして機能する。また図５−Ｂに示すように、排気弁の有効バルブ開口面積μｅ Ａｅ が吸気弁の有効バルブ開口面積μｉ Ａｉ よりも小さいときには、排気弁が絞りとして機能する。すなわち、排気弁及び吸気弁のうち、有効バルブ開口面積μＡの小さい方が絞りとして機能することとなる。したがって、有効バルブ開口面積の時間積分値Σ（μＡ）は、式（８）で表される。
【００４５】
【数８】

ここで吸気弁、排気弁の流量係数が同じと見なせるのであれば（μｉ ＝μｅ ＝μ）、同式（８）は更に式（９）のように表すことができる。なお式（９）の右辺括弧内は、図６にハッチングで示されるバルブリフト曲線の部分の面積、すなわちバルブオーバーラップ時間面積を示している。
【００４６】
【数９】

ここで吸気弁や排気弁の開閉時期、すなわちバルブタイミングを可変とする可変動弁機構を備える内燃機関の場合、上記バルブオーバーラップ時間面積は、吸排気弁のバルブタイミングの設定状況に応じて変化する。ただし、瞬時毎の有効バルブ開口面積μＡは、カムプロフィール等の設計諸元により決まるため、上記時間積分値Σ（μＡ）を、吸排気弁のバルブオーバーラップ量ＯＬと機関回転速度ＮＥの関数として求めることができる。すなわち有効バルブ開口面積μＡをクランク角について積分すれば、バルブオーバーラップ量ＯＬのみによる関数ｆ１（ＯＬ）が得られるようになる。そして、そのクランク角積分値を機関回転速度ＮＥで除算すれば、バルブオーバーラップ時間面積を、すなわち有効バルブ開口面積の時間積分値Σ（μＡ）を求めることができる。したがって上式（９）は、式（１０）により表すことができる。更にこの式（１０）を上式（７）に代入すれば、式（１１）が得られる。
【００４７】
【数１０】

【００４８】
【数１１】

（内部ＥＧＲ量ＭｅｇｒＡＬＬの算出）
燃焼時にシリンダ内に存在する内部ＥＧＲ量ＭｅｇｒＡＬＬは、上式（２）により表される残留既燃ガス量Ｍｅｇｒ１と上式（１１）により表される吹返し既燃ガス量Ｍｅｇｒ２との和として、式（１２）により求められるようになる。
【００４９】
【数１２】

なお排気管圧力Ｐｅ及び排気温度Ｔｅは、機関運転状態より推定可能であり、機関回転速度ＮＥと機関負荷との関数として求めることができる。したがって、排気管圧力Ｐｅ、及び排気温度Ｔｅを常に計測、又は推定しないのであれば、例えば機関負荷率ＫＬ（全負荷ＷＯＴに対する現在の負荷の割合）、吸入空気量ＧＡ、吸気管圧力Ｐｍ等のような機関負荷を表すパラメータと機関回転速度ＮＥとの関数としてそれらを求めるようにすれば良い。
【００５０】
例えば機関負荷の指標値として吸気管圧力Ｐｍを用いた場合、上式（１１）は式（１３）に示すように、バルブオーバーラップ量ＯＬ、機関回転速度ＮＥ、及び吸気管圧力Ｐｍの関数として表すことができる。図７は、そうした関数ｆ_３（ＮＥ，Ｐｍ）の設定態様の一例を示している。
【００５１】
【数１３】

また同様に上式（２）の｛Ｐｅ／（Ｒｅ・Ｔｅ）｝を機関回転速度ＮＥ、及び吸気管圧力Ｐｍの関数ｆ_４（ＮＥ，Ｐｍ）として与えると、残留既燃ガス量Ｍｅｇｒ１は式（１４）で表すことができる。
【００５２】
【数１４】

このような場合、内部ＥＧＲ量ＭｅｇｒＡＬＬは、式（１５）に示すように、機関回転速度ＮＥ、吸気管圧力Ｐｍ、バルブオーバーラップ量ＯＬ、吸気弁開時期Ｔｏｐｅｎの関数により求めることができる。
【００５３】
【数１５】

［点火時期のＶＶＴ補正量ＡＶＶＴの算出］
以上のように任意の機関運転状況における内部ＥＧＲ量は、機関回転速度ＮＥ、吸気管圧力Ｐｍ、及び吸排気弁のバルブオーバーラップ量ＯＬ（或いはバルブオーバーラップ面積ＡＯＬ）等を用いて表されることが確かめられた。この関係からは、以下のような、可変動弁機構１１ｍ，１１ｅの作動に応じた内部ＥＧＲ量の変化に応じた点火時期の補正態様が導き出される。
【００５４】
図８は、任意の機関回転速度、及び機関負荷における内部ＥＧＲ量の変化に応じた最適な点火時期ｔＳＡの変化態様を示している。同図８に示すように内部ＥＧＲ量が増大すれば、最適な点火時期ｔＳＡはより早い時期となる。これは、内部ＥＧＲ量の増大に応じてシリンダ内の燃料の燃焼速度が低下すること、等による。
【００５５】
さて、吸排気弁のバルブタイミングが、機関回転速度及び機関負荷から一義的に求められるのであれば、内部ＥＧＲ量も機関回転速度及び機関負荷より一義的に求めることができる。しかしながら機関運転中には、吸排気弁のバルブタイミングの変更に伴う可変動弁機構１１ｍ，１１ｅの応答遅れ等のため、実バルブタイミングＶＴｍ，ＶＴｅが目標バルブタイミングｔＶＴｍ，ｔＶＴｅと不一致となることがある。よって、点火時期をそのときの内部ＥＧＲ量に即して適正に補正するには、そうした実バルブタイミングＶＴｍ，ＶＴｅと目標バルブタイミングｔＶＴｍ，ｔＶＴｅとのずれによる内部ＥＧＲ量の変化を考慮する必要がある。
【００５６】
ここで内部ＥＧＲ量が”０”であるときの最適な点火時期を「基準点火時期ｔＳＡ０」といい、吸排気弁の実バルブタイミングＶＴｍ，ＶＴｅが目標バルブタイミングｔＶＴｍｂ，ｔＶＴｅｂにあるときの内部ＥＧＲ量を「目標内部ＥＧＲ量ｔＥＧＲ」という。また内部ＥＧＲ量が目標内部ＥＧＲ量ｔＥＧＲであるときの最適な点火時期ｔＳＡｂと上記基準点火時期ｔＳＡ０との差を「ベース補正量ＡＶＶＴｂ」という。これら「基準点火時期ｔＳＡ０」、「目標内部ＥＧＲ量ｔＥＧＲ」、及び「ベース補正量ＡＶＶＴｂ」はいずれも、機関回転速度と機関負荷とから一義的に求めることができる。また「目標内部ＥＧＲ量ｔＥＧＲ」、「ベース補正量ＡＶＶＴｂ」の機関回転速度及び機関負荷に対する相関関係は、予め実験等により求めておくことができる。
【００５７】
これらの「基準点火時期ｔＳＡ０」、「目標内部ＥＧＲ量ｔＥＧＲ」、及び「ベース補正量ＡＶＶＴｂ」を用いれば、上記点火時期ｔＳＡｂは、式（１６）で表すことができる。
【００５８】
【数１６】

更に同図８に示されるように、最適な点火時期ｔＳＡと内部ＥＧＲ量とが線形関係にあるとすれば、可変動弁機構１１ｍ，１１ｅの作動による内部ＥＧＲ量の変化に応じた点火時期の補正量であるＶＶＴ補正量ＡＶＶＴを、式（１７）に示すように与えることができる。すなわち、ＶＶＴ補正量ＡＶＶＴを、内部ＥＧＲ量の現状値である実内部ＥＧＲ量ｒｅａｌＥＧＲと、上記目標内部ＥＧＲ量ｔＥＧＲとの比ｒ_ｅｇｒ（＝ｒｅａｌＥＧＲ／ｔＥＧＲ）に比例した値として与えることができる。
【００５９】
【数１７】

ここで、任意の機関運転状況での内部ＥＧＲ量ＭｅｇｒＡＬＬは、上式（１）に示されるように残留既燃ガス量Ｍｅｇｒ１と吹返し既燃ガス量Ｍｅｇｒ２との和として表すことができる。よって上記比ｒ_ｅｇｒは、式（１８）のように表すことができる。なお式（１８）において、「ｒｅａｌＭｅｇｒ１」及び「ｒｅａｌＭｅｇｒ２」は、残留既燃ガス量、及び吹返し既燃ガス量の現状値をそれぞれ示している。また「ｔＭｅｇｒ１」及び「ｔＭｅｇｒ２」は、吸排気弁のバルブタイミングがその目標バルブタイミングｔＶＴｍ，ｔＶＴｅに収束されているときの残留既燃ガス量、及び吹返し既燃ガス量をそれぞれ示している。
【００６０】
【数１８】

なお、吸気弁開時にシリンダ内に存在する残留既燃ガスは、非常に高温でガス密度が低いことから、一般に残留既燃ガス量Ｍｅｇｒ１は、吹返し既燃ガス量Ｍｅｇｒ２に比して著しく小さい値となる（Ｍｅｇｒ１＜＜Ｍｅｇｒ２）。よって上記のような比をとった場合、上式（１８）は、式（１９）のように近似することができる。
【００６１】
【数１９】

ここで上式（１３）に示される吹返し既燃ガス量Ｍｅｇｒ２に係る式を、上式（１９）に代入すれば、式（２０）が得られる。なお式（２０）において「ｒｅａｌＯＬ」、「ｒｅａｌＮＥ」及び「ｒｅａｌＰｍ」は、バルブオーバーラップ量、機関回転速度、及び吸気管圧力の現状値をそれぞれ示している。また「ｔＯＬ」、「ｔＮＥ」及び「ｔＰｍ」は、吸排気弁のバルブタイミングがその目標バルブタイミングｔＶＴｍ，ｔＶＴｅに収束されているときのバルブオーバーラップ量、機関回転速度、及び吸気管圧力をそれぞれ示している。
【００６２】
【数２０】

一方、吸排気弁のバルブタイミングの過渡的な変化は、機関回転速度ＮＥ、及び吸気管圧力Ｐｍに直ちに影響を与える訳ではないため、バルブタイミング変更中の機関回転速度ＮＥ、及び吸気管圧力Ｐｍは、ほぼ一定と見なすことができる。よって、ｒｅａｌＮＥ＝ｔＮＥ、ｒｅａｌＰｍ＝ｔＰｍとなり、上式（２０）は更に式（２１）のように簡易化できる。
【００６３】
【数２１】

なお上述したように関数ｆ_１（ＯＬ）は、吸排気弁のバルブオーバーラップ面積ＡＯＬを示している。よって、上記比ｒ_ｅｇｒは、バルブオーバーラップ面積の現状値である実バルブオーバーラップ面積ｒｅａｌＡＯＬと、吸排気弁のバルブタイミングがその制御目標に収束されているときのバルブオーバーラップ面積である目標バルブオーバーラップ面積ｔＡＯＬとの比として表すことができる。
【００６４】
一方、図９に示すように、バルブオーバーラップ量ＯＬが変化しても、オーバーラップ部分ＡＯＬ１、ＡＯＬ２の形状は、ほぼ相似となっている。そこでオーバーラップ部分ＡＯＬ１、ＡＯＬ２の形状がバルブオーバーラップ量の変化に拘わらず相似であると見なせば、任意のバルブオーバーラップ量ＯＬについて、バルブオーバーラップ面積ＡＯＬは、そのバルブオーバーラップ量ＯＬの二乗に比例するとの近似が可能である。よって上式（２１）は、更に式（２２）のように表すことができる。
【００６５】
【数２２】

式（２１）、（２２）を上式（１７）に代入すれば、式（２３）、（２４）が得られる。すなわち、点火時期のＶＶＴ補正量ＡＶＶＴは、実バルブオーバーラップ面積ｒｅａｌＡＯＬと目標バルブオーバーラップ面積ｔＡＯＬとの比、或いは実バルブオーバーラップ量ｒｅａｌＯＬの平方数と目標バルブオーバーラップ量ｔＯＬの平方数との比に基づいて求めることができる。
【００６６】
【数２３】

【００６７】
【数２４】

図１０は、上式（２４）により示される、特定の機関回転速度及び特定の機関負荷における点火時期のＶＶＴ補正量ＡＶＶＴとバルブオーバーラップ量ＯＬとの関係を示している。同図１０に示されるように、機関回転速度、機関負荷が一定のときのＶＶＴ補正量ＡＶＶＴは、実バルブオーバーラップ量ｒｅａｌＯＬの平方数に比例した値となる。
【００６８】
本実施形態では、電子制御装置２０は、点火時期の設定に際して、上式（２４）を用いて算出されたＶＶＴ補正量ＡＶＶＴによる点火時期の補正を行っている。以下、そうした本実施形態でのＶＶＴ補正量ＡＶＶＴの算出態様について、図１１を併せ参照して説明する。
【００６９】
図１１は、ＶＶＴ補正量ＡＶＶＴの算出に係る処理態様をブロック図として示したものである。同図に示すように本処理においては、上述したバルブタイミング制御において設定された吸排気弁の目標バルブタイミングｔＶＴｍ，ｔＶＴｅより、目標バルブオーバーラップ量ｔＯＬが算出される。上記のようにバルブタイミング制御においては、目標バルブタイミングｔＶＴｍ，ｔＶＴｅは、機関回転速度ＮＥ及び機関負荷率ＫＬに基づき算出されている。同図の例では、機関回転速度ＮＥ及び機関負荷率ＫＬと吸排気弁の目標バルブタイミングｔＶＴｍ，ｔＶＴｅとの相関関係がそれぞれ記憶された演算マップＭ０１，Ｍ０２を用いて、目標バルブタイミングｔＶＴｍ，ｔＶＴｅが算出されている。
【００７０】
またこれとともに、カム角センサ２２ｍ，２２ｅの検出結果から吸排気弁の実バルブタイミングＶＴｍ，ＶＴｅが求められる。そして求められた吸排気弁の実バルブタイミングＶＴｍ，ＶＴｅに基づき、実バルブオーバーラップ量ｒｅａｌＯＬが算出される。
【００７１】
更に機関回転速度ＮＥ、及び機関負荷率ＫＬに基づいて、上記ベース補正量ＡＶＶＴｂが算出される。ここでは、ベース補正量ＡＶＶＴｂの算出は、機関回転速度ＮＥ及び機関負荷率ＫＬとベース補正量ＡＶＶＴｂとの相関関係が記憶された演算マップＭ０３を用いて行われている。
【００７２】
上記のように算出されたベース補正量ＡＶＶＴｂ、目標バルブオーバーラップ量ｔＯＬ、及び実バルブオーバーラップ量ｒｅａｌＯＬから、上式（２４）に従ってＶＶＴ補正量ＡＶＶＴが算出される。そしてその算出されたＶＶＴ補正量ＡＶＶＴを用いて点火時期の補正が行われる。これにより、可変動弁機構１１ｍ，１１ｅの作動に伴う内部ＥＧＲ量の変化に応じた適切な点火時期の設定がなされることとなる。
【００７３】
以上説明した本実施形態によれば、以下の効果を奏することができる。
（１）本実施形態では、実バルブオーバーラップ量ｒｅａｌＯＬの平方数と目標バルブオーバーラップ量ｔＯＬの平方数との比に基づいて点火時期のＶＶＴ補正量ＡＶＶＴを算出している。ここで、上記平方数の比は、上式（２２）に示されるように、実内部ＥＧＲ量ｒｅａｌＥＧＲと目標内部ＥＧＲ量ｔＥＧＲとの比を表している。そのため、上記算出されたＶＶＴ補正量ＡＶＶＴを用いることで、可変動弁機構１１ｍ，１１ｅの作動に伴う内部ＥＧＲ量の変化に応じた点火時期の補正を容易且つ適切に行うことができる。
【００７４】
なお、内部ＥＧＲ量の増減に応じてシリンダ内に導入される新気の量が変化するため、新気の量の厳密な制御が求められる場合などには、内部ＥＧＲ量の変化に応じて吸入空気量やスロットル開度を補正することがある。またそうした新気導入量の変化に対応した空燃比の制御等のため、内部ＥＧＲ量の変化に応じた燃料噴射量の補正が必要となることがある。更に内部ＥＧＲ量の変化による燃焼状態の変化への対応等のため、内部ＥＧＲ量の変化に応じた燃料噴射時期の補正が必要となることや、外部ＥＧＲを行う内燃機関でのシリンダ内に存在する既燃ガス量の制御等のため、内部ＥＧＲ量の変化に応じた外部ＥＧＲ量の補正が必要となることがある。
【００７５】
このような可変動弁機構の作動に伴う内部ＥＧＲ量の変化の影響を受ける、点火時期以外の機関制御量の補正についても、実バルブオーバーラップ面積と目標バルブオーバーラップ面積との比や、実バルブオーバーラップ量の平方数と目標バルブオーバーラップ量の平方数との比に基づき算出することもできる。
【００７６】
（第２実施形態）
続いて、本発明の内燃機関の制御装置を具体化した第２実施形態を、第１実施形態と異なる点を中心に説明する。
【００７７】
上式（２１）によれば、実内部ＥＧＲ量ｒｅａｌＥＧＲと目標内部ＥＧＲ量ｔＥＧＲとの比ｒ_ｅｇｒ が、実バルブオーバーラップ面積ｒｅａｌＡＯＬと目標バルブオーバーラップ面積ｔＡＯＬとの比に等しいことが示されている。また上式（２２）によれば、同比ｒ_ｅｇｒ が、更に実バルブオーバーラップ量ｒｅａｌＯＬの平方数と目標バルブオーバーラップ量ｔＯＬの平方数との比に等しいことが示されている。これらの関係からは、次の式（２５）、（２６）の関係が導き出せる。すなわち内部ＥＧＲ量ＭｅｇｒＡＬＬは、バルブオーバーラップ面積ＡＯＬに比例し、又はバルブオーバーラップ量ＯＬの平方数に比例する。ここで「ｋ１」、「ｋ２」はそれぞれ、所定の定数を示している。
【００７８】
【数２５】

【００７９】
【数２６】

これらの関係により、可変動弁機構１１ｍ，１１ｅの作動状態、特にその作動に応じて設定されるバルブオーバーラップ面積ＡＯＬやバルブオーバーラップ量ＯＬと、内部ＥＧＲ量との関係を的確に把握することができる。例えば図１２に示すように、内部ＥＧＲ量ＭｅｇｒＡＬＬを現状の１／４に減量する場合には、バルブオーバーラップ量ＯＬを現状の１／２とすれば良い。
【００８０】
よって、次の（ａ）、（ｂ）のように可変動弁機構１１ｍ，１１ｅを制御することで、容易且つ確実に内部ＥＧＲ量を目標内部ＥＧＲ量ｔＥＧＲへと調整することができる。
（ａ）吸排気弁のバルブオーバーラップ面積ＡＯＬが、実内部ＥＧＲ量ｒｅａｌＥＧＲに対する目標内部ＥＧＲ量ｔＥＧＲの比と実バルブオーバーラップ面積ｒｅａｌＡＯＬとの乗算値となるように可変動弁機構１１ｍ，１１ｅを制御する。
（ｂ）吸排気弁のバルブオーバーラップ量ＯＬが、実内部ＥＧＲ量ｒｅａｌＥＧＲに対する目標内部ＥＧＲ量ｔＥＧＲの比の平方根と実バルブオーバーラップ量ｒｅａｌＯＬとの乗算値となるように可変動弁機構１１ｍ，１１ｅを制御する。
【００８１】
また、上式（２５）、（２６）からは、次の式（２７）、（２８）に示される関係を導き出すことができる。ここで基本バルブオーバーラップ面積ｂａｓｅＡＯＬ、基本バルブオーバーラップ量ｂａｓｅＯＬ、及び基本ＥＧＲ量ｂａｓｅＥＧＲは、吸排気弁が基本目標バルブタイミングｔｂＶＴｍ，ｔｂＶＴｅにあるときのバルブオーバーラップ面積、バルブオーバーラップ量、及び内部ＥＧＲ量をそれぞれ示している。
【００８２】
【数２７】

【００８３】
【数２８】

基本バルブオーバーラップ面積ｂａｓｅＡＯＬ、基本バルブオーバーラップ量ｂａｓｅＯＬは、基本目標バルブタイミングｔｂＶＴｍ，ｔｂＶＴｅによって一義的に決まるため、機関回転速度、機関負荷から一義的に求めることができる。また基本ＥＧＲ量ｂａｓｅＥＧＲも、機関回転速度及び機関負荷から一義的に決めることができ、予め実験等で求めておくこともできる。
【００８４】
こうした式（２７）、（２８）によれば、内部ＥＧＲ量を所望の値とするために必要なバルブオーバーラップ面積、及びバルブオーバーラップ量を容易且つ適切に求めることができる。すなわち、同式（２７）又は式（２８）により算出された目標バルブオーバーラップ面積ｔＡＯＬ又は目標バルブオーバーラップ量ｔＯＬが得られるように可変動弁機構１１ｍ，１１ｅを制御すれば、高精度の内部ＥＧＲ量の調整を容易に行うことができる。
【００８５】
以下、そうした内部ＥＧＲ量の調整を、内部ＥＧＲのリミット制御に適用した例を説明する。
図１３に、本実施形態での「内部ＥＧＲのリミット制御ルーチン」のフローチャートを示す。本ルーチンの処理は、定時割り込み処理として電子制御装置２０により周期的に実行される。
【００８６】
本ルーチンに処理が移行されると、まずステップ１００において、吸排気弁の基本目標バルブタイミングｔｂＶＴｍ，ｔｂＶＴｅがそれぞれ算出される。ここでの算出は、予め電子制御装置２０に記憶された、機関回転速度ＮＥと機関負荷とに基づく演算マップを用いて行われる。また同ステップ１００において、算出された基本目標バルブタイミングｔｂＶＴｍ，ｔｂＶＴｅから基本バルブオーバーラップ量ｂａｓｅＯＬが算出される。基本バルブオーバーラップ量ｂａｓｅＯＬは、吸排気弁のバルブタイミングが共に基本目標バルブタイミングｔｂＶＴｍ，ｔｂＶＴｅにあるときのバルブオーバーラップ量を示している。
【００８７】
ステップ１１０では、機関回転速度ＮＥ及び機関負荷率ＫＬに基づき、基本ＥＧＲ量ｂａｓｅＥＧＲが算出される。基本ＥＧＲ量ｂａｓｅＥＧＲは、吸排気弁のバルブタイミングが基本目標バルブタイミングｔｂＶＴｍ，ｔｂＶＴｅとなっていることを前提とした現状の機関回転速度ＮＥ及び機関負荷率ＫＬでの内部ＥＧＲ量を示している。
【００８８】
ステップ１２０では、機関回転速度ＮＥの推移に基づいて内燃機関１０のトルク変動量ΔＴＬが算出される。そしてステップ１３０において、その算出されたトルク変動量ΔＴＬが判定値α以上であるか否かが判定される。判定値αは、許容されるトルク変動量ΔＴＬの上限値よりも、すなわち燃焼の不安定化を示すトルク変動量ΔＴＬの下限値よりも若干小さい値に設定されている。
【００８９】
ここでトルク変動量ΔＴＬが判定値α以上であれば（ステップ１３０において「ＹＥＳ」）、ステップ１４０において、内部ＥＧＲ減量値ΔＥＧＲに所定値γが加算される。またトルク変動量ΔＴＬが判定値α未満であれば（ステップ１３０において「ＮＯ」）、ステップ１５０において、内部ＥＧＲ減量値ΔＥＧＲから所定値βが減算される。この所定値βは、所定値γに比して小さい値が設定されている。
【００９０】
内部ＥＧＲ減量値ΔＥＧＲは、基本ＥＧＲ量ｂａｓｅＥＧＲから減らすべき内部ＥＧＲの量を示している。ちなみに内部ＥＧＲ減量値ΔＥＧＲが負の値となるときには、内部ＥＧＲ量が基本ＥＧＲ量ｂａｓｅＥＧＲよりも増やされる。
【００９１】
こうして内部ＥＧＲ減量値ΔＥＧＲが設定されると、続くステップ１６０において、式（２９）に基づいて、基本ＥＧＲ量ｂａｓｅＥＧＲ及び内部ＥＧＲ減量値ΔＥＧＲから目標内部ＥＧＲ量ｔＥＧＲが算出される。
【００９２】
【数２９】

図１４に、以上の処理による目標内部ＥＧＲ量ｔＥＧＲの設定態様の一例を示す。同図に示すように、目標内部ＥＧＲ量ｔＥＧＲは、トルク変動量ΔＴＬが判定値α未満であるときには、所定値βずつ徐々に増やされる。一方、内部ＥＧＲ量が過剰となり、燃焼が不安定となってトルク変動量ΔＴＬが判定値α以上となると（同図の時刻ｔ１，ｔ２）、目標内部ＥＧＲ量ｔＥＧＲは所定値γ分、大きく減らされる。これにより、目標内部ＥＧＲ量ｔＥＧＲは、燃焼の不安定化を招かない内部ＥＧＲ量の範囲の上限近傍まで増大されるようになる。
【００９３】
よって、内部ＥＧＲ量がこの目標内部ＥＧＲ量ｔＥＧＲとなるように可変動弁機構１１ｍ，１１ｅを制御すれば、好ましい燃焼状態が維持できる範囲内で、できるだけ多くの内部ＥＧＲを導入して、燃料消費率の低減や排気エミッション性能の向上を図ることができる。そうした内部ＥＧＲ量の調整に必要な可変動弁機構１１ｍ，１１ｅの目標バルブタイミングｔＶＴｍ，ｔＶＴｅの算出は、続くステップ１７０及び１８０で行われる。
【００９４】
ステップ１７０では、次の式（３０）を用いてリミット補正量ΔＯＬが算出される。このリミット補正量ΔＯＬは、図１５に示すように、基本バルブオーバーラップ量ｂａｓｅＯＬと目標バルブオーバーラップ量ｔＯＬとの差（ｂａｓｅＯＬ−ｔＯＬ）を示している。
【００９５】
【数３０】

続くステップ１８０では、このリミット補正量ΔＯＬだけバルブオーバーラップ量が少なくなるように基本目標バルブタイミングｔｂＶＴｍ，ｔｂＶＴｅを補正して最終的な目標バルブタイミングｔＶＴｍ，ｔＶＴｅが算出される。ここでは、排気弁の基本目標バルブタイミングｔｂＶＴｅをリミット補正量ΔＶＴだけ進角側に補正してその最終的な目標バルブタイミングｔＶＴｅとしている（ｔＶＴｅ＝ｂａｓｅＶＴｅ＋ΔＯＬ）。その一方、吸気弁については、基本目標バルブタイミングｔｂＶＴｍがそのまま最終的な目標バルブタイミングｔＶＴｍとされている（ｔＶＴｍ＝ｂａｓｅＶＴｍ）。
【００９６】
電子制御装置２０は、こうして吸排気弁の最終的な目標バルブタイミングｔＶＴｍ，ｔＶＴｅを設定して本ルーチンの処理を一旦終了する。こうして設定された最終的な目標バルブタイミングｔＶＴｍ，ｔＶＴｅに基づき可変動弁機構１１ｍ，１１ｅが制御されると、吸排気弁のバルブオーバーラップ量ＯＬが上記目標バルブオーバーラップ量ｔＯＬとなり、内部ＥＧＲ量が上記算出された目標内部ＥＧＲ量ｔＥＧＲに調整されるようになる。
【００９７】
以上説明した本実施形態によれば、次の効果を奏することができる。
（１）本実施形態では、基本ＥＧＲ量ｂａｓｅＥＧＲに対する目標内部ＥＧＲ量ｔＥＧＲの比の平方根と基本バルブオーバーラップ量ｂａｓｅＯＬとの乗算値である目標バルブオーバーラップ量ｔＯＬが得られるように可変動弁機構１１ｍ，１１ｅを制御している。そしてこれにより、内部ＥＧＲ量を目標内部ＥＧＲ量ｔＥＧＲに調整するようにしている。このように本実施形態では、式（２２）等に示される内部ＥＧＲ量とバルブオーバーラップ量との関係に基づき可変動弁機構１１ｍ，１１ｅを制御して内部ＥＧＲ量を調整している。そのため、内部ＥＧＲ量の調整を高精度に行うことができる。
【００９８】
以上の各実施形態は、以下のように変更して実施することもできる。
・図１１の算出ロジックでは、実バルブオーバーラップ量ｒｅａｌＯＬ及び目標バルブオーバーラップ量ｔＯＬに基づき、式（２４）を用いてＶＶＴ補正量ＡＶＶＴを算出しているが、その算出に式（２３）を用いるようにしても良い。このときの実バルブオーバーラップ面積ｒｅａｌＡＯＬ及び目標バルブオーバーラップ面積ｔＡＯＬは、吸排気弁のバルブタイミングの目標値や現状値から求めることができる。こうした場合、バルブオーバーラップ面積ＡＯＬがバルブオーバーラップ量ＯＬの平方数に比例すると見なすことができない構成にも、その適用が可能となる。
【００９９】
・図１３の内部ＥＧＲのリミット制御ルーチンでは、式（２８）に示されるバルブオーバーラップ量と内部ＥＧＲ量との関係に基づいて、吸排気弁の目標バルブタイミングｔＶＴｍ，ｔＶＴｅを算出している。この算出を、式（２７）に示されるバルブオーバーラップ面積と内部ＥＧＲ量との関係に基づいて行うようにしても良い。こうした場合には、バルブオーバーラップ面積ＡＯＬがバルブオーバーラップ量ＯＬの平方数に比例すると見なすことができない構成にも、その適用が可能となる。
【０１００】
・第１実施形態でのＶＶＴ補正量ＡＶＶＴの算出を、式（１５）等を用いて実内部ＥＧＲ量ｒｅａｌＥＧＲ及び目標内部ＥＧＲ量ｔＥＧＲをそれぞれ求め、式（１７）に示されるように実内部ＥＧＲ量ｒｅａｌＥＧＲと目標内部ＥＧＲ量ｔＥＧＲとの比に基づいて行うようにしても良い。
【０１０１】
・第２実施形態での内部ＥＧＲ量の調整に係る可変動弁機構の制御は、可変動弁機構によるバルブオーバーラップ状態の変更を通じて内部ＥＧＲ量の調整を行う制御であれば、内部ＥＧＲのリミット制御以外の制御にも同様、或いはそれに準じた態様で適用することができる。いずれにせよ、式（２１）、（２２）に示される関係に基づき可変動弁機構１１ｍ，１１ｅの制御を行えば、高精度の内部ＥＧＲ量の調整を容易に行うことができる。
【０１０２】
・上記各実施形態では、吸排気弁のバルブタイミングをそれぞれ可変とする２つの可変動弁機構１１ｍ，１１ｅを備える内燃機関１０への本発明の適用例を示したが、吸排気弁のいずれか一方のみに可変動弁機構を備える内燃機関に本発明をすることもできる。また、バルブリフト量を可変とする機構等の他のタイプの可変動弁機構を備える内燃機関にも本発明の適用は可能である。要は、可変動弁機構により吸排気弁のバルブオーバーラップ状態が可変とされる内燃機関であれば、本発明を適用することができる。
【０１０３】
上記各実施形態及びその変更例から把握される技術的思想を、以下に列記する。
（イ）機関回転速度及び機関負荷より設定された基本目標作動量に基づいて、吸排気弁のバルブオーバーラップ状態を可変とする可変動弁機構を備え、その可変動弁機構の作動により内部ＥＧＲ量を変更する内燃機関に適用されて、該可変動弁機構の作動に伴う内部ＥＧＲ量の変化に応じて所定の機関制御量を補正する内燃機関の制御装置において、機関回転速度及び機関負荷より算出されたベース補正量に対して、実内部ＥＧＲ量と目標内部ＥＧＲ量との比を乗算して、前記所定の機関制御量の補正に係る補正量を算出することを特徴とする内燃機関の制御装置。
【０１０４】
（ロ）機関回転速度及び機関負荷より設定された基本目標作動量に基づいて、吸排気弁のバルブオーバーラップ状態を可変とする可変動弁機構を備える内燃機関に適用されて、該可変動弁機構の作動に伴う内部ＥＧＲ量の変化に応じて所定の機関制御量を補正する内燃機関の制御装置において、機関回転速度及び機関負荷より算出されたベース補正量に対して、実バルブオーバーラップ面積と目標バルブオーバーラップ面積との比をそのベース補正量に乗算して、前記所定の機関制御量の補正に係る補正量を算出することを特徴とする内燃機関の制御装置。
【０１０５】
（ハ）機関回転速度及び機関負荷より設定された基本目標作動量に基づいて、吸排気弁のバルブオーバーラップ状態を可変とする可変動弁機構を備える内燃機関に適用されて、該可変動弁機構の作動に伴う内部ＥＧＲ量の変化に応じて所定の機関制御量を補正する内燃機関の制御装置において、機関回転速度及び機関負荷より算出されたベース補正量に対して、実バルブオーバーラップ量の平方数と目標バルブオーバーラップ量の平方数との比を乗算して、前記所定の機関制御量の補正に係る補正量を算出することを特徴とする内燃機関の制御装置。
【０１０６】
（ニ）前記機関制御量は、点火時期である請求項１〜３、及び上記（イ）〜（ハ）のいずれかに記載の内燃機関の制御装置。
（ホ）前記機関制御量は、吸入空気量である請求項１〜３、及び上記（イ）〜（ハ）のいずれかに記載の内燃機関の制御装置。
【０１０７】
（ヘ）前記機関制御量は、燃料噴射量である請求項１〜３、及び上記（イ）〜（ハ）のいずれかに記載の内燃機関の制御装置。
（ト）前記機関制御量は、燃料噴射時期である請求項１〜３、及び上記（イ）〜（ハ）のいずれかに記載の内燃機関の制御装置。
【０１０８】
（チ）前記機関制御量は、外部ＥＧＲ量である請求項１〜３、及び上記（イ）〜（ハ）のいずれかに記載の内燃機関の制御装置。
（リ）前記目標内部ＥＧＲ量は、当該機関のトルク変動の度合いに応じて算出される請求項４〜７のいずれかに記載の内燃機関の制御装置。
【図面の簡単な説明】
【図１】本発明の第１実施形態についてその全体構造を示す模式図。
【図２】同実施形態のバルブタイミングの設定例を示すグラフ。
【図３】内燃機関における既燃ガスの挙動を示す模式図。
【図４】排気管からの既燃ガスの吹返しについてのモデル図。
【図５】排気管から吹き返す既燃ガスの挙動を示す模式図。
【図６】吸排気弁のバルブリフト量の推移を示すグラフ。
【図７】関数ｆ_３（ＮＥ，Ｐｍ）の設定例を示すグラフ。
【図８】内部ＥＧＲ量と最適な点火時期との対応関係例を示すグラフ。
【図９】バルブオーバーラップ量の変化に応じたバルブリフト曲線の変化を示すグラフ。
【図１０】実バルブオーバーラップ量とＶＶＴ補正量との関係を示すグラフ。
【図１１】第１実施形態でのＶＶＴ補正量算出ロジックのブロック図。
【図１２】バルブオーバーラップ量に応じた内部ＥＧＲ量の変化を示すグラフ。
【図１３】第２実施形態における内部ＥＧＲのリミット制御ルーチンのフローチャート。
【図１４】同ルーチンによる目標ＥＧＲ量の制御例を示すタイムチャート。
【図１５】バルブオーバーラップ量に応じた内部ＥＧＲ量の変化を示すグラフ。
【符号の説明】
１０…内燃機関、１１ｍ，１１ｅ…可変動弁機構、１２…インジェクタ、１３…スロットルバルブ、１４…点火プラグ、２０…電子制御装置、２１…クランク角センサ、２２ｍ，２２ｅ…カム角センサ、２３…吸気管圧力センサ、２４…エアフローメータ。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a control device for controlling an internal combustion engine including a variable valve mechanism that makes a valve overlap state of intake and exhaust valves variable.
[0002]
[Prior art]
In recent years, for the purpose of improving intake efficiency, improving exhaust emissions by reducing NOx, and improving fuel efficiency by reducing pumping loss in accordance with the introduction of internal EGR, the valve characteristics of intake and exhaust valves have been adjusted according to the engine operating conditions. 2. Description of the Related Art An internal combustion engine with a variable valve mechanism that is variable has been put to practical use. For example, in an in-vehicle internal combustion engine, a variable valve timing mechanism that varies the opening / closing timing of intake and exhaust valves, that is, a valve timing, and a variable valve lift mechanism that varies the valve lift amount of intake and exhaust valves are widely used as variable valve operating mechanisms. Has been adopted.
[0003]
In this type of internal combustion engine, the amount of internal EGR present in the cylinder increases or decreases according to the operation of the variable valve mechanism such as a change in the valve overlap state of the intake and exhaust valves. Therefore, it is necessary to set the engine control amount such as the ignition timing in consideration of the change in the internal EGR amount according to the operation of the variable valve mechanism. Conventionally, as a control device for an internal combustion engine that sets an ignition timing in consideration of a change in an internal EGR amount according to the operation of such a variable valve mechanism, a control device described in Patent Literature 1 is known.
[0004]
[Patent Document 1]
JP-A-9-209895
[0005]
[Problems to be solved by the invention]
The internal EGR amount varies in a complicated manner according to the engine speed, the engine load, and the operating state of the variable valve mechanism. However, in the above-described conventional control device, the operating state of the variable valve mechanism, the change in the internal EGR amount, Is not clear, and it is difficult to set an appropriate ignition timing for a change in the internal EGR amount.
[0006]
In addition, since the operation of the variable valve mechanism causes a change in the internal EGR amount, it is considered that the internal EGR amount can be controlled by the operation of the variable valve mechanism, but the above relationship is unclear. As described above, it is impossible to control the internal EGR amount with high accuracy.
[0007]
The present invention has been made in view of such circumstances, and an object thereof is to provide an internal combustion engine capable of easily and appropriately performing engine control based on a relationship between an operation state of a variable valve mechanism and a change in an internal EGR amount. An object of the present invention is to provide an engine control device.
[0008]
[Means for Solving the Problems]
Hereinafter, means for achieving the above-described object and the effects thereof will be described.
The invention according to claim 1 is applied to an internal combustion engine in which the internal EGR amount can be adjusted by a variable valve mechanism that makes the valve overlap state of the intake and exhaust valves variable, and the internal pressure associated with the operation of the variable valve mechanism. In a control device for an internal combustion engine that corrects a predetermined engine control amount according to a change in an EGR amount, a correction amount related to the correction of the predetermined engine control amount is determined based on a ratio between an actual internal EGR amount and a target internal EGR amount. The gist is to calculate.
[0009]
In the above configuration, for example, the valve overlap of the intake and exhaust valves is made variable by a variable valve operating mechanism that makes the valve timing and the valve lift of at least one of the intake valve and the exhaust valve variable. When the valve overlap of the intake and exhaust valves is changed by the operation of the variable valve mechanism, the internal EGR amount of the internal combustion engine changes. As a result, the engine control variable affected by the change in the internal EGR amount, such as the ignition timing, the throttle opening, the fuel injection amount, the fuel injection timing, and the external EGR amount, also changes.
[0010]
At this time, in the above configuration, the ratio of the actual internal EGR amount, which is the current value of the internal EGR amount, to the target internal EGR amount, which is the internal EGR amount when the operation amount of the variable valve mechanism converges to its control target, The engine control amount is corrected by the correction amount calculated based on the above. That is, in the above-described configuration, the index value indicating the degree of change of the internal EGR amount due to the operation of the variable valve mechanism is determined not by the change amount of the internal EGR amount but by the ratio of the actual internal EGR amount to the target internal EGR amount. Correction for the engine control amount is performed. Therefore, the influence of the change in the internal EGR amount is more easily and accurately reflected in the correction of the engine control amount. Therefore, according to the above configuration, it is possible to easily and accurately correct the engine control amount according to the change in the internal EGR amount accompanying the operation of the variable valve mechanism.
[0011]
The invention according to claim 2 is applied to an internal combustion engine including a variable valve operating mechanism of a variable valve operating mechanism that makes a valve overlap state of an intake / exhaust valve variable, and an internal part accompanying the operation of the variable valve operating mechanism In a control device for an internal combustion engine that corrects a predetermined engine control amount according to a change in an EGR amount, a correction amount relating to the correction of the predetermined engine control amount is determined by a ratio of an actual valve overlap area to a target valve overlap area. The gist is to calculate based on.
[0012]
As shown in Expression (21), it can be said that the ratio between the actual internal EGR amount and the target internal EGR amount is equal to the ratio between the actual valve overlap area and the target valve overlap area. Therefore, as in the above configuration, the correction amount for the predetermined engine control amount according to the change in the internal EGR amount accompanying the operation of the variable valve mechanism is determined based on the ratio between the actual valve overlap area and the target valve overlap area. By calculating, it is possible to easily and accurately correct the engine control amount according to the change in the internal EGR amount accompanying the operation of the variable valve mechanism.
[0013]
The invention according to claim 3 is applied to an internal combustion engine including a variable valve operating mechanism of a variable valve operating mechanism that makes a valve overlap state of an intake / exhaust valve variable, and an internal part accompanying the operation of the variable valve operating mechanism In a control device for an internal combustion engine that corrects a predetermined engine control amount according to a change in an EGR amount, the correction amount relating to the correction of the predetermined engine control amount is determined by calculating a square number of an actual valve overlap amount and a target valve overlap amount. The gist is to calculate based on the ratio to the square number of.
[0014]
The valve overlap area can be approximated as being proportional to the square number of the valve overlap amount. Therefore, as shown in Expression (22), it can be said that the ratio between the actual internal EGR amount and the target internal EGR amount is equal to the ratio between the square number of the actual valve overlap amount and the square number of the target valve overlap amount. . Therefore, as in the above configuration, the correction amount for the predetermined engine control amount according to the change in the internal EGR amount accompanying the operation of the variable valve operating mechanism is determined by the square number of the actual valve overlap amount and the square number of the target valve overlap amount. By calculating based on the ratio, the engine control amount can be easily and accurately corrected in accordance with the change in the internal EGR amount accompanying the operation of the variable valve mechanism.
[0015]
The invention according to claim 4 is applied to an internal combustion engine provided with a variable valve mechanism that makes the valve overlap state of the intake and exhaust valves variable, and controls the internal EGR amount through changing the valve overlap state. In the control device, the variable valve mechanism is controlled such that the valve overlap area of the intake / exhaust valve is a product of the ratio of the target internal EGR amount to the actual internal EGR amount and the actual valve overlap area. That is the gist.
[0016]
As shown in Expression (21), it can be said that the ratio between the actual internal EGR amount and the target internal EGR amount is equal to the ratio between the actual valve overlap area and the target valve overlap area. Therefore, if the variable valve mechanism is controlled such that the valve overlap area of the intake / exhaust valve is a product of the ratio of the target internal EGR amount to the actual internal EGR amount and the actual valve overlap area as in the above configuration. , The internal EGR amount can be set as the target internal EGR amount. Therefore, according to the above configuration, the internal EGR amount can be adjusted with high accuracy based on the operation control of the variable valve mechanism.
[0017]
The invention according to claim 5 is applied to an internal combustion engine provided with a variable valve mechanism that makes the valve overlap state of the intake and exhaust valves variable, and controls the internal EGR amount by changing the valve overlap state. Controlling the variable valve mechanism so that the valve overlap amount of the intake / exhaust valve is a product of the square root of the ratio of the target internal EGR amount to the actual internal EGR amount and the actual valve overlap amount. The main point is to do.
[0018]
As shown in equation (22), it can be said that the ratio between the actual internal EGR amount and the target internal EGR amount is equal to the ratio between the square number of the actual valve overlap amount and the square number of the target valve overlap amount. it can. As described above, if the variable valve mechanism is controlled so that the valve overlap amount of the intake and exhaust valves is a product of the square root of the ratio of the target internal EGR amount to the actual internal EGR amount and the actual valve overlap amount. , The internal EGR amount can be set as the target internal EGR amount. Therefore, according to the above configuration, the internal EGR amount can be adjusted with high accuracy based on the operation control of the variable valve mechanism.
[0019]
Further, the invention according to claim 6 is applied to an internal combustion engine having a variable valve operating mechanism that makes the valve overlap state of the intake and exhaust valves variable, and controls the internal EGR amount by changing the valve overlap state. In the control device of the engine, the basic valve overlap area uniquely set based on the engine speed and the engine load, and the internal EGR amount when the valve overlap area of the intake and exhaust valves is the basic valve overlap area. Based on a basic internal EGR amount and a target internal EGR amount which is a control target value of the internal EGR amount, a value obtained by multiplying a value obtained by multiplying a ratio of the target internal EGR amount to the basic internal EGR amount by the basic valve overlap area is applied to the valve Controlling the internal EGR amount by controlling the variable valve mechanism as a control target value of the overlap area; The door and the gist thereof.
[0020]
From the equation (21) and the like, the relationship shown in the equation (27) can be derived. Based on this relationship, the valve overlap area required for making the internal EGR amount the target internal EGR amount is determined as a product of the ratio of the target internal EGR amount to the basic internal EGR amount and the basic valve overlap area. Can be. Therefore, according to the above configuration, the internal EGR amount can be adjusted with high accuracy based on the operation control of the variable valve mechanism.
[0021]
Further, the invention according to claim 7 is applied to an internal combustion engine having a variable valve mechanism for making the valve overlap state of the intake and exhaust valves variable, and controlling the internal EGR amount through changing the valve overlap state. In the engine control device, the basic valve overlap amount uniquely set based on the engine speed and the engine load, and the internal EGR amount when the valve overlap amount of the intake and exhaust valves is the basic valve overlap amount. Based on a basic internal EGR amount and a target internal EGR amount which is a control target value of the internal EGR amount, a multiplication value of a square root of a ratio of the target internal EGR amount to the basic internal EGR amount and the basic valve overlap amount is calculated. By controlling the variable valve mechanism as the control target value of the valve overlap amount, the internal EGR amount is controlled. It is referred to as the gist thereof.
[0022]
From the equation (22) and the like, the relation shown in the equation (28) can be derived. Based on this relationship, the valve overlap amount necessary to make the internal EGR amount the target internal EGR amount is calculated by multiplying the square root of the ratio of the target internal EGR amount to the basic internal EGR amount by the basic valve overlap amount. You can ask. Therefore, according to the above configuration, the internal EGR amount can be adjusted with high accuracy based on the operation control of the variable valve mechanism.
[0023]
BEST MODE FOR CARRYING OUT THE INVENTION
(1st Embodiment)
Hereinafter, a first embodiment of a control device for an internal combustion engine according to the present invention will be described in detail with reference to the drawings.
[0024]
As shown in FIG. 1, an internal combustion engine 10 to which the present embodiment is applied is provided with various sensors for detecting an engine operating condition. For example, a crank angle sensor 21 is provided near a crankshaft which is an output shaft of the internal combustion engine 10. Cam angle sensors 22m and 22e are provided near the intake and exhaust camshafts, respectively. Further, an intake pipe pressure sensor 23 and an air flow meter 24 as a flow rate sensor are provided in an intake pipe of the internal combustion engine 10. The detection signals of these sensors are input to an electronic control unit 20 that controls various controls of the internal combustion engine 10.
[0025]
The electronic control unit 20 grasps the engine operation status based on the detection signals of such sensors. For example, from the detection signal of the crank angle sensor 21, the rotational phase of the crank shaft, that is, the crank angle is obtained, and further the engine rotational speed NE is calculated. From the detection signals of the cam angle sensors 22m and 22e, the rotational phases of the intake and exhaust camshafts, that is, the cam angles, are obtained. Further, an intake pipe pressure Pm is obtained from a detection signal of the intake pipe pressure sensor 23, and an intake air amount GA is obtained from a detection signal of the air flow meter 24.
[0026]
The electronic control unit 20 performs various controls of the internal combustion engine 10 based on the engine operation status obtained from the detection results of the sensors described above. For example, the electronic control unit 20 outputs a command signal to the injector 12, the ignition plug 14, and the throttle valve 13 of the internal combustion engine 10 in accordance with the engine operation state, and performs fuel injection control, ignition timing control, and intake air amount control. I have.
[0027]
The internal combustion engine 10 is configured as an internal combustion engine with a variable valve mechanism including two variable valve mechanisms 11m and 11e that make valve timings of an intake valve and an exhaust valve respectively variable. In this embodiment, the variable valve mechanisms 11m and 11e change the valve timings of the intake valves and the exhaust valves by changing the relative rotation phases of the camshafts on the intake side and the exhaust side with respect to the crankshaft that is the output shaft of the engine. Is adopted.
[0028]
The electronic control unit 20 performs valve timing control for varying the valve timing of the intake and exhaust valves based on the drive control of the variable valve mechanisms 11m and 11e. The valve timing control in the present embodiment is performed by the electronic control device 20 in the following procedure.
[0029]
First, based on the engine speed NE and the engine load, target valve timings tVTm and tVTe, which are control target values of the valve timings of the intake valve and the exhaust valve, are calculated. The variable valve mechanisms 11m and 11e are driven such that the actual valve timings realVTm and realVTe of the intake and exhaust valves detected by the cam angle sensors 22m and 22e become the obtained target valve timings tVTm and tVTe, respectively.
[0030]
In the present embodiment, the valve timings of the intake and exhaust valves are represented using the advance amount (VTm) and the retard amount (VTe) shown in FIG. That is, the valve timing VTe of the intake valve is based on the most retarded position at which the opening and closing of the intake valve is the slowest in the variable range of the valve timing by the variable valve mechanism 11m, and the amount of advance from the most retarded position. [° CA]. Further, the valve timing VTe of the exhaust valve is based on the most advanced position where the opening and closing of the exhaust valve is the fastest in the variable range of the valve timing by the variable valve mechanism 11e, and the amount of retardation from the most retarded position. [° CA].
[0031]
When the valve timing of the intake and exhaust valves is changed in this manner, the internal EGR amount increases and decreases, and the optimal ignition timing changes. Therefore, in the present embodiment, the ignition timing is corrected in consideration of a change in the internal EGR amount due to a change in the valve timing of the intake and exhaust valves by the variable valve mechanisms 11m and 11e. Hereinafter, the manner of correcting the ignition timing in this embodiment will be described.
[0032]
[Calculation of Internal EGR Amount MegrALL]
First, calculation of the internal EGR amount MegrALL in an arbitrary engine operating state will be described. As described above, the internal EGR amount MegrALL changes in accordance with the operating conditions of the variable valve mechanisms 11m and 11e in addition to the engine speed NE and the engine load. Such a change in the internal EGR amount MegrALL can be easily and accurately grasped by using the valve overlap area AOL or the valve overlap amount OL of the intake / exhaust valve as described below.
[0033]
(Behavior of burned gas in cylinder)
Here, the behavior of the burned gas in the cylinder of the internal combustion engine 10 will be considered.
The burned gas generated in the cylinder by the combustion of the fuel is discharged to an exhaust pipe according to the opening of the exhaust valve (see FIG. 3-A). Thereafter, when the intake valve is opened and the valve overlap is started, the burned gas is blown back into the cylinder from the exhaust pipe due to the differential pressure between the exhaust pipe pressure Pe and the intake pipe pressure Pm (FIG. 3). -C). At this time, some burned gas flows through the cylinder and flows into the intake pipe, but such burned gas is re-introduced into the cylinder together with fresh air in a subsequent intake stroke. Here, the burned gas introduced into the cylinder by the blow-back from the exhaust pipe during the valve overlap period after the opening of the intake valve is referred to as "burn-back burned gas", and the amount thereof is referred to as "burn-back burned gas". Amount Megr2 ".
[0034]
On the other hand, immediately before the intake valve is opened, a certain amount of burned gas remains in the cylinder without being discharged to the exhaust pipe (see FIG. 3-B). A part of the burned gas continues to stay in the cylinder as it is, and the remaining part flows out once into the intake pipe due to the return of exhaust gas during valve overlap, and is then re-introduced into the cylinder during the intake stroke. . Therefore, any burned gas remaining in the cylinder immediately before the opening of the intake valve is, in any case, present in the cylinder at the time of combustion. Here, the burned gas remaining in the cylinder immediately before the opening of the intake valve is referred to as “residual burned gas”, and the amount thereof is referred to as “residual burned gas amount Megr1”.
[0035]
Therefore, the internal EGR amount MegrALL existing in the cylinder at the time of combustion can be obtained as the sum of the residual burned gas amount Megr1 and the blown back burned gas amount Megr2 as shown in Expression (1).
[0036]
(Equation 1)

(Calculation of residual burned gas amount Megr1)
The residual burned gas amount Megr1 can be represented by a gas state equation based on the state in the cylinder immediately before the intake valve opens as shown in Expression (2). Here, Pm: intake pipe pressure, Pe: exhaust pipe pressure, Re: gas constant of burned gas, Te: exhaust temperature, and V: cylinder volume immediately before opening the intake valve.
[0037]
(Equation 2)

Further, the cylinder volume V immediately before the intake valve is opened is based on the intake valve opening timing Topen (BTDC), the cylinder bore diameter rb, the piston stroke S, and the volume of the combustion chamber when the piston is at the top dead center, that is, the clearance volume Vc. It is determined by equation (3).
[0038]
[Equation 3]

In the above equation (3), the cylinder bore diameter rb, the stroke S, and the clearance volume Vc are constants determined by design specifications and the like. Therefore, in the case of an internal combustion engine provided with a variable valve mechanism that makes the valve timing of the intake and exhaust valves variable, the cylinder volume V is a function f of the intake valve opening timing Topen. ₂ (Topen).
[0039]
(Calculation of the burned-back burned gas amount Megr2)
During the valve overlap period, the burned gas flows from the exhaust pipe toward the intake pipe due to the differential pressure between the exhaust pipe pressure Pe and the intake pipe pressure Pm, and the burned gas in the exhaust pipe is blown back into the cylinder. Become. At this time, in the burned gas flow path, the opening of the intake / exhaust valve is a throttle whose flow path area is locally narrowed. Accordingly, the aspect of the flow of the burned gas at this time can be represented by a model as shown in FIG. 4, and the flow rate Q can be obtained by using a flow rate calculation formula of the throttle.
[0040]
Here, equation (4) is used as the equation for calculating the flow rate of the throttle. Here, κ: specific heat ratio of burned gas, μ: flow coefficient, and A: valve opening area.
[0041]
(Equation 4)

Φ (Pm / Pe) in the above equation (4) is expressed by the equation (5) when 1 / (κ + 1) <Pm / Pe.
[0042]
(Equation 5)

On the other hand, when 1 / (κ + 1) ≧ Pm / Pe, Φ (Pm / Pe) in the above equation (4) is expressed by the equation (6).
[0043]
(Equation 6)

Therefore, the amount of burned gas introduced into the cylinder by the return of exhaust gas, that is, the amount of burnt-back burned gas Megr2 can be obtained as a time integrated value of the burned gas flow rate of such a throttle in the valve overlap period. . Furthermore, since the intake pipe pressure Pm, the exhaust pipe pressure Pe, the exhaust temperature Te, and the specific heat ratio κ of the burned gas do not change rapidly, their values during the valve overlap can be regarded as constant. Therefore, the blown back burned gas amount Megr2 can be obtained as a value proportional to the time integral value Σ (μA) of the effective valve opening area μA (= flow coefficient μ × valve opening area A). Therefore, the blown back burned gas amount Megr2 can be expressed by the equation (7).
[0044]
(Equation 7)

(Calculation of time integral value of effective valve opening area Σ (μA))
As shown in FIG. 5A, when the exhaust gas is blown back during the valve overlap period, when the effective valve opening area μi Ai of the intake valve is smaller than the effective valve opening area μe Ae of the exhaust valve, the intake valve functions as a throttle. I do. Also, as shown in FIG. 5B, when the effective valve opening area μe Ae of the exhaust valve is smaller than the effective valve opening area μi Ai of the intake valve, the exhaust valve functions as a throttle. That is, the smaller of the effective valve opening area μA of the exhaust valve and the intake valve functions as a throttle. Therefore, the time integral value Σ (μA) of the effective valve opening area is represented by Expression (8).
[0045]
(Equation 8)

Here, if the flow coefficients of the intake valve and the exhaust valve can be considered to be the same (μi = μe = μ), the equation (8) can be further expressed as the equation (9). Note that the area in parentheses on the right side of the equation (9) indicates the area of the valve lift curve indicated by hatching in FIG. 6, that is, the valve overlap time area.
[0046]
(Equation 9)

Here, in the case of an internal combustion engine having a variable valve mechanism for varying the opening / closing timing of the intake valve and the exhaust valve, that is, the valve timing, the valve overlap time area changes according to the setting state of the valve timing of the intake / exhaust valve. I do. However, since the effective valve opening area μA at each instant is determined by design specifications such as a cam profile, the above time integral value Σ (μA) is used as a function of the valve overlap amount OL of the intake and exhaust valves and the engine speed NE. You can ask. That is, by integrating the effective valve opening area μA with respect to the crank angle, a function f1 (OL) based on only the valve overlap amount OL can be obtained. Then, by dividing the crank angle integral value by the engine rotational speed NE, the valve overlap time area, that is, the time integral value Σ (μA) of the effective valve opening area can be obtained. Therefore, the above equation (9) can be expressed by equation (10). Further, by substituting equation (10) into equation (7), equation (11) is obtained.
[0047]
(Equation 10)

[0048]
[Equation 11]

(Calculation of internal EGR amount MegrALL)
The internal EGR amount MegrALL present in the cylinder at the time of combustion is the sum of the residual burned gas amount Megr1 represented by the above equation (2) and the blown back burned gas amount Megr2 represented by the above equation (11). This is obtained by the equation (12).
[0049]
(Equation 12)

The exhaust pipe pressure Pe and the exhaust gas temperature Te can be estimated from the operating state of the engine, and can be obtained as a function of the engine speed NE and the engine load. Therefore, if the exhaust pipe pressure Pe and the exhaust temperature Te are not always measured or estimated, for example, the engine load factor KL (the ratio of the current load to the full load WOT), the intake air amount GA, the intake pipe pressure Pm, etc. Such a parameter may be obtained as a function of the parameter representing the engine load and the engine speed NE.
[0050]
For example, when the intake pipe pressure Pm is used as an index value of the engine load, the above equation (11) is a function of the valve overlap amount OL, the engine rotation speed NE, and the intake pipe pressure Pm as shown in the equation (13). Can be represented. FIG. 7 shows such a function f ₃ An example of a setting mode of (NE, Pm) is shown.
[0051]
(Equation 13)

Similarly, {Pe / (Re · Te)} in the above equation (2) is used to calculate the function f of the engine speed NE and the intake pipe pressure Pm. ₄ When given as (NE, Pm), the residual burned gas amount Megr1 can be expressed by equation (14).
[0052]
[Equation 14]

In such a case, the internal EGR amount MegrALL can be determined by a function of the engine speed NE, the intake pipe pressure Pm, the valve overlap amount OL, and the intake valve opening timing Topen, as shown in Expression (15).
[0053]
(Equation 15)

[Calculation of VVT correction amount AVVT of ignition timing]
As described above, the internal EGR amount in an arbitrary engine operating condition is represented by using the engine rotation speed NE, the intake pipe pressure Pm, the valve overlap amount OL (or the valve overlap area AOL) of the intake and exhaust valves, and the like. It was confirmed. From this relationship, the following correction mode of the ignition timing according to the change of the internal EGR amount according to the operation of the variable valve mechanisms 11m and 11e is derived.
[0054]
FIG. 8 shows how the optimum ignition timing tSA changes according to the change in the internal EGR amount at an arbitrary engine speed and an arbitrary engine load. As shown in FIG. 8, if the internal EGR amount increases, the optimal ignition timing tSA becomes earlier. This is because the combustion speed of the fuel in the cylinder decreases as the internal EGR amount increases.
[0055]
Now, if the valve timing of the intake and exhaust valves can be uniquely determined from the engine speed and the engine load, the internal EGR amount can also be uniquely determined from the engine speed and the engine load. However, during engine operation, the actual valve timings VTm, VTe may not match the target valve timings tVTm, tVTe due to a response delay of the variable valve mechanisms 11m, 11e due to a change in the valve timing of the intake and exhaust valves. is there. Therefore, in order to properly correct the ignition timing in accordance with the internal EGR amount at that time, it is necessary to consider a change in the internal EGR amount due to such a deviation between the actual valve timings VTm, VTe and the target valve timings tVTm, tVTe. is there.
[0056]
Here, the optimum ignition timing when the internal EGR amount is “0” is referred to as “reference ignition timing tSA0”, and the internal EGR when the actual valve timings VTm and VTe of the intake and exhaust valves are at the target valve timings tVTmb and tVTeb. The amount is referred to as “target internal EGR amount tEGR”. The difference between the optimal ignition timing tSAb and the reference ignition timing tSA0 when the internal EGR amount is the target internal EGR amount tEGR is referred to as “base correction amount AVVTb”. These “reference ignition timing tSA0”, “target internal EGR amount tEGR”, and “base correction amount AVVTb” can all be uniquely obtained from the engine speed and the engine load. The correlation between the "target internal EGR amount tEGR" and the "base correction amount AVVTb" with respect to the engine speed and the engine load can be obtained in advance by experiments or the like.
[0057]
Using these “reference ignition timing tSA0”, “target internal EGR amount tEGR”, and “base correction amount AVVTb”, the ignition timing tSAb can be expressed by equation (16).
[0058]
(Equation 16)

Further, as shown in FIG. 8, assuming that the optimal ignition timing tSA and the internal EGR amount are in a linear relationship, the ignition timing according to the change in the internal EGR amount due to the operation of the variable valve mechanisms 11m and 11e. The VVT correction amount AVVT, which is the correction amount, can be given as shown in Expression (17). That is, the VVT correction amount AVVT is determined by the ratio r between the actual internal EGR amount realEGR, which is the current value of the internal EGR amount, and the target internal EGR amount tEGR. _egr (= RealEGR / tEGR).
[0059]
[Equation 17]

Here, the internal EGR amount MegrALL in an arbitrary engine operating condition can be represented as the sum of the residual burned gas amount Megr1 and the blown back burned gas amount Megr2 as shown in the above equation (1). Therefore, the above ratio r _egr Can be expressed as in equation (18). In Expression (18), “realMegr1” and “realMegr2” indicate the current values of the residual burned gas amount and the blown back burned gas amount, respectively. “TMegr1” and “tMegr2” respectively indicate the residual burned gas amount and the blown back burned gas amount when the valve timing of the intake / exhaust valve is converged to the target valve timings tVTm and tVTe.
[0060]
(Equation 18)

Since the residual burned gas present in the cylinder when the intake valve is open is very high temperature and has a low gas density, the residual burned gas amount Megr1 is generally significantly smaller than the blown back burned gas amount Megr2. Value (Megr1 << Megr2). Therefore, when the above ratio is taken, the above equation (18) can be approximated as the equation (19).
[0061]
[Equation 19]

Here, by substituting the equation relating to the blown back burned gas amount Megr2 shown in the above equation (13) into the above equation (19), the equation (20) is obtained. In the equation (20), “realOL”, “realNE”, and “realPm” indicate the current values of the valve overlap amount, the engine rotation speed, and the intake pipe pressure, respectively. “TOL”, “tNE”, and “tPm” represent the valve overlap amount, the engine speed, and the intake pipe pressure when the valve timings of the intake and exhaust valves converge to the target valve timings tVTm, tVTe, respectively. Is shown.
[0062]
(Equation 20)

On the other hand, since a transient change in the valve timing of the intake and exhaust valves does not immediately affect the engine speed NE and the intake pipe pressure Pm, the engine speed NE and the intake pipe pressure Pm during the valve timing change are not changed. Can be considered almost constant. Therefore, realNE = tNE, realPm = tPm, and the above equation (20) can be further simplified as equation (21).
[0063]
(Equation 21)

Note that the function f ₁ (OL) indicates the valve overlap area AOL of the intake and exhaust valves. Therefore, the ratio r _egr Is the actual valve overlap area realAOL, which is the current value of the valve overlap area, and the target valve overlap area tAOL, which is the valve overlap area when the valve timing of the intake and exhaust valves is converged on the control target. It can be expressed as a ratio.
[0064]
On the other hand, as shown in FIG. 9, even if the valve overlap amount OL changes, the shapes of the overlap portions AOL1 and AOL2 are substantially similar. Therefore, if it is considered that the shapes of the overlap portions AOL1 and AOL2 are similar regardless of the change in the valve overlap amount, the valve overlap area AOL is determined by the value of the valve overlap amount OL for an arbitrary valve overlap amount OL. An approximation that is proportional to the square is possible. Therefore, the above equation (21) can be further expressed as equation (22).
[0065]
(Equation 22)

By substituting equations (21) and (22) into equation (17), equations (23) and (24) are obtained. That is, the VVT correction amount AVVT of the ignition timing is determined by the ratio between the actual valve overlap area realAOL and the target valve overlap area tAOL, or the square number of the actual valve overlap amount realOL and the square number of the target valve overlap amount tOL. It can be determined based on the ratio.
[0066]
[Equation 23]

[0067]
(Equation 24)

FIG. 10 shows the relationship between the VVT correction amount AVVT of the ignition timing at a specific engine speed and a specific engine load, and the valve overlap amount OL, which is expressed by the above equation (24). As shown in FIG. 10, the VVT correction amount AVVT when the engine rotation speed and the engine load are constant is a value proportional to the square of the actual valve overlap amount realOL.
[0068]
In the present embodiment, when setting the ignition timing, the electronic control unit 20 corrects the ignition timing using the VVT correction amount AVVT calculated using the above equation (24). Hereinafter, the manner of calculating the VVT correction amount AVVT in this embodiment will be described with reference to FIG.
[0069]
FIG. 11 is a block diagram showing a processing mode relating to the calculation of the VVT correction amount AVVT. As shown in the figure, in this processing, the target valve overlap amount tOL is calculated from the target valve timings tVTm and tVTe of the intake and exhaust valves set in the above-described valve timing control. As described above, in the valve timing control, the target valve timings tVTm and tVTe are calculated based on the engine speed NE and the engine load factor KL. In the example shown in the figure, the target valve timings tVTm and tVTe are calculated using the calculation maps M01 and M02 in which the correlations between the engine speed NE and the engine load factor KL and the target valve timings tVTm and tVTe of the intake and exhaust valves are stored. Is calculated.
[0070]
At the same time, actual valve timings VTm and VTe of the intake and exhaust valves are obtained from the detection results of the cam angle sensors 22m and 22e. Then, the actual valve overlap amount realOL is calculated based on the obtained actual valve timings VTm and VTe of the intake and exhaust valves.
[0071]
Further, the base correction amount AVVTb is calculated based on the engine speed NE and the engine load factor KL. Here, the calculation of the base correction amount AVVTb is performed using the calculation map M03 in which the correlation between the engine speed NE and the engine load factor KL and the base correction amount AVVTb is stored.
[0072]
From the base correction amount AVVTb, the target valve overlap amount tOL, and the actual valve overlap amount realOL calculated as described above, the VVT correction amount AVVT is calculated according to the above equation (24). Then, the ignition timing is corrected using the calculated VVT correction amount AVVT. As a result, an appropriate ignition timing is set according to a change in the internal EGR amount due to the operation of the variable valve mechanisms 11m and 11e.
[0073]
According to the embodiment described above, the following effects can be obtained.
(1) In the present embodiment, the VVT correction amount AVVT of the ignition timing is calculated based on the ratio of the square number of the actual valve overlap amount realOL to the square number of the target valve overlap amount tOL. Here, the ratio of the square numbers represents the ratio between the actual internal EGR amount realEGR and the target internal EGR amount tEGR, as shown in the above equation (22). Therefore, by using the calculated VVT correction amount AVVT, it is possible to easily and appropriately correct the ignition timing according to the change in the internal EGR amount due to the operation of the variable valve mechanisms 11m and 11e.
[0074]
In addition, since the amount of fresh air introduced into the cylinder changes according to the increase or decrease of the internal EGR amount, when strict control of the amount of fresh air is required, the intake air is changed according to the change of the internal EGR amount. The air amount and throttle opening may be corrected. Further, in order to control the air-fuel ratio in response to such a change in the fresh air introduction amount, it may be necessary to correct the fuel injection amount in accordance with the change in the internal EGR amount. Further, in order to cope with a change in the combustion state due to a change in the internal EGR amount, it is necessary to correct the fuel injection timing in accordance with the change in the internal EGR amount. In some cases, the external EGR amount needs to be corrected according to the change in the internal EGR amount for controlling the burned gas amount.
[0075]
Regarding the correction of the engine control amount other than the ignition timing, which is affected by the change of the internal EGR amount due to the operation of the variable valve mechanism, the ratio of the actual valve overlap area to the target valve overlap area and the actual It can also be calculated based on the ratio between the square number of the valve overlap amount and the square number of the target valve overlap amount.
[0076]
(2nd Embodiment)
Next, a second embodiment that embodies the control device for an internal combustion engine of the present invention will be described focusing on differences from the first embodiment.
[0077]
According to the above equation (21), the ratio r between the actual internal EGR amount realEGR and the target internal EGR amount tEGR _egr Is equal to the ratio of the actual valve overlap area realAOL to the target valve overlap area tAOL. According to the above equation (22), the same ratio r _egr Is further equal to the ratio of the square number of the actual valve overlap amount realOL to the square number of the target valve overlap amount tOL. From these relationships, the following relationships of Expressions (25) and (26) can be derived. That is, the internal EGR amount MegrALL is proportional to the valve overlap area AOL or proportional to the square of the valve overlap amount OL. Here, “k1” and “k2” each indicate a predetermined constant.
[0078]
(Equation 25)

[0079]
(Equation 26)

Based on these relationships, it is possible to accurately grasp the operating state of the variable valve mechanisms 11m and 11e, particularly the relationship between the valve overlap area AOL and the valve overlap amount OL set according to the operation and the internal EGR amount. Can be. For example, as shown in FIG. 12, when the internal EGR amount MegrALL is reduced to １ ／ of the current value, the valve overlap amount OL may be set to の of the current value.
[0080]
Therefore, the internal EGR amount can be easily and reliably adjusted to the target internal EGR amount tEGR by controlling the variable valve mechanisms 11m and 11e as in the following (a) and (b).
(A) The variable valve mechanisms 11m and 11e are set so that the valve overlap area AOL of the intake and exhaust valves is a product of the ratio of the target internal EGR amount tEGR to the actual internal EGR amount realEGR and the actual valve overlap area realAOL. Control.
(B) The variable valve mechanism 11m, so that the valve overlap amount OL of the intake / exhaust valve is a product of the square root of the ratio of the target internal EGR amount tEGR to the actual internal EGR amount realEGR and the actual valve overlap amount realOL. 11e.
[0081]
From the above equations (25) and (26), the relations shown in the following equations (27) and (28) can be derived. Here, the basic valve overlap area baseAOL, the basic valve overlap amount baseOL, and the basic EGR amount baseEGR are the valve overlap area, the valve overlap amount, and the internal when the intake and exhaust valves are at the basic target valve timings tbVTm, tbVTe. The respective EGR amounts are shown.
[0082]
[Equation 27]

[0083]
[Equation 28]

Since the basic valve overlap area baseAOL and the basic valve overlap amount baseOL are uniquely determined by the basic target valve timings tbVTm and tbVTe, they can be uniquely determined from the engine speed and the engine load. The basic EGR amount base EGR can also be uniquely determined from the engine speed and the engine load, and can be obtained in advance through experiments or the like.
[0084]
According to the equations (27) and (28), the valve overlap area and the valve overlap amount necessary for setting the internal EGR amount to a desired value can be easily and appropriately obtained. That is, if the variable valve mechanisms 11m and 11e are controlled such that the target valve overlap area tAOL or the target valve overlap amount tOL calculated by the equation (27) or the equation (28) is obtained, a highly accurate internal The adjustment of the EGR amount can be easily performed.
[0085]
Hereinafter, an example in which the adjustment of the internal EGR amount is applied to the internal EGR limit control will be described.
FIG. 13 shows a flowchart of the “internal EGR limit control routine” in the present embodiment. The process of this routine is periodically executed by the electronic control unit 20 as a periodic interrupt process.
[0086]
When the process proceeds to this routine, first, in step 100, basic target valve timings tbVTm and tbVTe of the intake and exhaust valves are calculated. The calculation here is performed using a calculation map based on the engine speed NE and the engine load, which is stored in the electronic control unit 20 in advance. In step 100, the basic valve overlap amount baseOL is calculated from the calculated basic target valve timings tbVTm and tbVTe. The basic valve overlap amount baseOL indicates the valve overlap amount when the valve timings of the intake and exhaust valves are both at the basic target valve timings tbVTm and tbVTe.
[0087]
In step 110, a basic EGR amount base EGR is calculated based on the engine speed NE and the engine load factor KL. The basic EGR amount base EGR indicates the internal EGR amount at the current engine rotational speed NE and the current engine load factor KL on the assumption that the valve timing of the intake and exhaust valves is the basic target valve timing tbVTm, tbVTe.
[0088]
In step 120, the torque fluctuation amount ΔTL of the internal combustion engine 10 is calculated based on the transition of the engine speed NE. Then, at step 130, it is determined whether or not the calculated torque variation ΔTL is equal to or greater than a determination value α. The determination value α is set to a value slightly smaller than the upper limit value of the allowable torque fluctuation amount ΔTL, that is, a value slightly smaller than the lower limit value of the torque fluctuation amount ΔTL indicating unstable combustion.
[0089]
Here, if torque variation ΔTL is equal to or greater than determination value α (“YES” in step 130), in step 140, a predetermined value γ is added to internal EGR decrease value ΔEGR. If torque variation ΔTL is smaller than determination value α (“NO” in step 130), in step 150, predetermined value β is subtracted from internal EGR decrease value ΔEGR. The predetermined value β is set to a value smaller than the predetermined value γ.
[0090]
The internal EGR decrease value ΔEGR indicates the amount of internal EGR to be reduced from the basic EGR amount base EGR. Incidentally, when the internal EGR decrease value ΔEGR becomes a negative value, the internal EGR amount is increased from the basic EGR amount baseEGR.
[0091]
When the internal EGR reduction value ΔEGR is set in this way, in the next step 160, the target internal EGR amount tEGR is calculated from the basic EGR amount base EGR and the internal EGR reduction value ΔEGR based on equation (29).
[0092]
(Equation 29)

FIG. 14 shows an example of a setting mode of the target internal EGR amount tEGR by the above processing. As shown in the figure, the target internal EGR amount tEGR is gradually increased by a predetermined value β when the torque variation ΔTL is less than the determination value α. On the other hand, when the internal EGR amount becomes excessive, combustion becomes unstable, and the torque fluctuation amount ΔTL becomes equal to or larger than the determination value α (time t1, t2 in the figure), the target internal EGR amount tEGR is greatly reduced by the predetermined value γ. It is. As a result, the target internal EGR amount tEGR is increased to near the upper limit of the internal EGR amount range that does not cause unstable combustion.
[0093]
Therefore, if the variable valve mechanisms 11m and 11e are controlled so that the internal EGR amount becomes equal to the target internal EGR amount tEGR, as much internal EGR as possible is introduced within a range where a preferable combustion state can be maintained, and fuel consumption is increased. The efficiency can be reduced and the exhaust emission performance can be improved. The calculation of the target valve timings tVTm and tVTe of the variable valve mechanisms 11m and 11e necessary for the adjustment of the internal EGR amount is performed in the following steps 170 and 180.
[0094]
In step 170, the limit correction amount ΔOL is calculated using the following equation (30). As shown in FIG. 15, the limit correction amount ΔOL indicates a difference (baseOL−tOL) between the basic valve overlap amount baseOL and the target valve overlap amount tOL.
[0095]
[Equation 30]

In the following step 180, the basic target valve timings tbVTm and tbVTe are corrected so that the valve overlap amount is reduced by the limit correction amount ΔOL, and the final target valve timings tVTm and tVTe are calculated. Here, the basic target valve timing tbVTe of the exhaust valve is corrected to the advance side by the limit correction amount ΔVT to obtain the final target valve timing tVTe (tVTe = baseVTe + ΔOL). On the other hand, for the intake valve, the basic target valve timing tbVTm is used as it is as the final target valve timing tVTm (tVTm = baseVTm).
[0096]
The electronic control unit 20 sets the final target valve timings tVTm and tVTe of the intake and exhaust valves in this way, and ends the processing of this routine once. When the variable valve mechanisms 11m and 11e are controlled based on the final target valve timings tVTm and tVTe thus set, the valve overlap amount OL of the intake and exhaust valves becomes the target valve overlap amount tOL, and the internal EGR amount Is adjusted to the calculated target internal EGR amount tEGR.
[0097]
According to the embodiment described above, the following effects can be obtained.
(1) In the present embodiment, the variable valve operating mechanism is configured to obtain a target valve overlap amount tOL which is a product of a square root of a ratio of the target internal EGR amount tEGR to the basic EGR amount baseEGR and the basic valve overlap amount baseOL. 11m and 11e are controlled. Thus, the internal EGR amount is adjusted to the target internal EGR amount tEGR. As described above, in the present embodiment, the internal EGR amount is adjusted by controlling the variable valve mechanisms 11m and 11e based on the relationship between the internal EGR amount and the valve overlap amount shown in Expression (22) and the like. Therefore, the adjustment of the internal EGR amount can be performed with high accuracy.
[0098]
Each of the above embodiments can be modified and implemented as follows.
In the calculation logic of FIG. 11, the VVT correction amount AVVT is calculated using the equation (24) based on the actual valve overlap amount realOL and the target valve overlap amount tOL, and the equation (23) is used for the calculation. It may be used. At this time, the actual valve overlap area realAOL and the target valve overlap area tAOL can be obtained from the target value and the current value of the valve timing of the intake and exhaust valves. In such a case, the present invention can be applied to a configuration in which the valve overlap area AOL cannot be regarded as being proportional to the square number of the valve overlap amount OL.
[0099]
In the internal EGR limit control routine of FIG. 13, the target valve timings tVTm and tVTe of the intake and exhaust valves are calculated based on the relationship between the valve overlap amount and the internal EGR amount shown in Expression (28). This calculation may be performed based on the relationship between the valve overlap area and the internal EGR amount shown in Expression (27). In such a case, the present invention can be applied to a configuration in which the valve overlap area AOL cannot be regarded as being proportional to the square of the valve overlap amount OL.
[0100]
In the calculation of the VVT correction amount AVVT in the first embodiment, the actual internal EGR amount realEGR and the target internal EGR amount tEGR are respectively obtained by using equation (15) and the like, and the actual internal EGR amount is calculated as shown in equation (17). The determination may be performed based on a ratio between the amount realEGR and the target internal EGR amount tEGR.
[0101]
The control of the variable valve mechanism relating to the adjustment of the internal EGR amount in the second embodiment is a limit of the internal EGR if the control is to adjust the internal EGR amount through the change of the valve overlap state by the variable valve mechanism. Control other than control can be applied in a similar or similar manner. In any case, if the control of the variable valve mechanisms 11m and 11e is performed based on the relationships shown in the equations (21) and (22), the internal EGR amount can be easily adjusted with high accuracy.
[0102]
In each of the above embodiments, the application example of the present invention to the internal combustion engine 10 including the two variable valve mechanisms 11m and 11e for respectively varying the valve timings of the intake and exhaust valves has been described. The present invention can also be applied to an internal combustion engine having a variable valve mechanism on only one side. Further, the present invention can be applied to an internal combustion engine having another type of variable valve mechanism such as a mechanism that makes the valve lift variable. In short, the present invention can be applied to any internal combustion engine in which the valve overlap state of the intake and exhaust valves is made variable by a variable valve mechanism.
[0103]
The technical ideas grasped from the above embodiments and the modified examples are listed below.
(A) A variable valve mechanism that varies the valve overlap state of the intake and exhaust valves based on the basic target operation amount set from the engine speed and the engine load, and the internal EGR is operated by the operation of the variable valve mechanism. A control device for an internal combustion engine applied to an internal combustion engine that changes the amount and corrects a predetermined engine control amount in accordance with a change in the internal EGR amount accompanying the operation of the variable valve mechanism. Multiplying the calculated base correction amount by a ratio of the actual internal EGR amount to the target internal EGR amount to calculate a correction amount related to the correction of the predetermined engine control amount; Control device.
[0104]
(B) applied to an internal combustion engine having a variable valve mechanism for varying the valve overlap state of the intake and exhaust valves based on a basic target operation amount set from the engine speed and the engine load; In a control device for an internal combustion engine, which corrects a predetermined engine control amount in accordance with a change in an internal EGR amount accompanying operation of a mechanism, an actual valve overlap area with respect to a base correction amount calculated from an engine speed and an engine load. A control device for an internal combustion engine, wherein a correction amount relating to the correction of the predetermined engine control amount is calculated by multiplying a ratio of the base correction amount to a target valve overlap area.
[0105]
(C) applied to an internal combustion engine having a variable valve mechanism for varying the valve overlap state of the intake and exhaust valves based on a basic target operation amount set from the engine speed and the engine load; In a control device for an internal combustion engine, which corrects a predetermined engine control amount according to a change in an internal EGR amount accompanying operation of a mechanism, an actual valve overlap amount is compared with a base correction amount calculated from an engine speed and an engine load. A multiplication of the ratio of the square number of the target valve overlap amount to the square number of the target valve overlap amount to calculate a correction amount related to the correction of the predetermined engine control amount.
[0106]
(D) The control device for an internal combustion engine according to any one of claims 1 to 3 and (a) to (c), wherein the engine control amount is an ignition timing.
(E) The control device for an internal combustion engine according to any one of (1) to (3) and (A) to (C), wherein the engine control amount is an intake air amount.
[0107]
(F) The control device for an internal combustion engine according to any one of (1) to (3) and (A) to (C), wherein the engine control amount is a fuel injection amount.
(G) The control device for an internal combustion engine according to any one of (1) to (3) and (A) to (C), wherein the engine control amount is a fuel injection timing.
[0108]
(H) The control device for an internal combustion engine according to any one of claims 1 to 3, and (a) to (c), wherein the engine control amount is an external EGR amount.
(I) The control device for an internal combustion engine according to any one of claims 4 to 7, wherein the target internal EGR amount is calculated according to a degree of torque fluctuation of the engine.
[Brief description of the drawings]
FIG. 1 is a schematic view showing the entire structure of a first embodiment of the present invention.
FIG. 2 is a graph showing a setting example of valve timing according to the embodiment;
FIG. 3 is a schematic diagram showing the behavior of burned gas in an internal combustion engine.
FIG. 4 is a model diagram showing the flareback of burned gas from an exhaust pipe.
FIG. 5 is a schematic diagram showing the behavior of burned gas blown back from an exhaust pipe.
FIG. 6 is a graph showing a change in a valve lift of an intake / exhaust valve.
FIG. 7: Function f ₃ 9 is a graph showing a setting example of (NE, Pm).
FIG. 8 is a graph showing an example of a correspondence relationship between an internal EGR amount and an optimal ignition timing.
FIG. 9 is a graph showing a change in a valve lift curve according to a change in a valve overlap amount.
FIG. 10 is a graph showing a relationship between an actual valve overlap amount and a VVT correction amount.
FIG. 11 is a block diagram of a VVT correction amount calculation logic in the first embodiment.
FIG. 12 is a graph showing a change in an internal EGR amount according to a valve overlap amount.
FIG. 13 is a flowchart of an internal EGR limit control routine according to the second embodiment.
FIG. 14 is a time chart showing an example of controlling the target EGR amount by the same routine.
FIG. 15 is a graph showing a change in an internal EGR amount according to a valve overlap amount.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Internal combustion engine, 11m, 11e ... Variable valve mechanism, 12 ... Injector, 13 ... Throttle valve, 14 ... Spark plug, 20 ... Electronic control unit, 21 ... Crank angle sensor, 22m, 22e ... Cam angle sensor, 23 ... Intake pipe pressure sensor, 24 ... air flow meter.

Claims (7)

The present invention is applied to an internal combustion engine in which the internal EGR amount can be adjusted by a variable valve mechanism that makes the valve overlap state of the intake and exhaust valves variable, and a predetermined value is set according to a change in the internal EGR amount accompanying the operation of the variable valve mechanism. In a control device for an internal combustion engine that corrects an engine control amount,
A control device for an internal combustion engine, wherein a correction amount related to the correction of the predetermined engine control amount is calculated based on a ratio between an actual internal EGR amount and a target internal EGR amount. The present invention is applied to an internal combustion engine including a variable valve operating mechanism of a variable valve operating mechanism that makes a valve overlap state of an intake / exhaust valve variable, and a predetermined engine is operated according to a change in an internal EGR amount accompanying the operation of the variable valve operating mechanism. In the control device of the internal combustion engine for correcting the control amount,
A control device for an internal combustion engine, wherein a correction amount related to the correction of the predetermined engine control amount is calculated based on a ratio between an actual valve overlap area and a target valve overlap area. The present invention is applied to an internal combustion engine including a variable valve operating mechanism of a variable valve operating mechanism that makes a valve overlap state of an intake / exhaust valve variable, and a predetermined engine is operated according to a change in an internal EGR amount accompanying the operation of the variable valve operating mechanism. In the control device of the internal combustion engine for correcting the control amount,
A control apparatus for an internal combustion engine, wherein a correction amount related to the correction of the predetermined engine control amount is calculated based on a ratio between a square number of an actual valve overlap amount and a square number of a target valve overlap amount. A control apparatus for an internal combustion engine, which is applied to an internal combustion engine having a variable valve operating mechanism that makes a valve overlap state of an intake and exhaust valve variable and controls an internal EGR amount through a change in the valve overlap state,
The variable valve mechanism is controlled such that a valve overlap area of the intake / exhaust valve is a product of a ratio of a target internal EGR amount to an actual internal EGR amount and an actual valve overlap area. Control device for internal combustion engine. A control apparatus for an internal combustion engine, which is applied to an internal combustion engine having a variable valve operating mechanism that makes a valve overlap state of an intake and exhaust valve variable and controls an internal EGR amount through a change in the valve overlap state,
The variable valve mechanism is controlled such that the valve overlap amount of the intake and exhaust valves is a product of the square root of the ratio of the target internal EGR amount to the actual internal EGR amount and the actual valve overlap amount. Control device for an internal combustion engine. A control apparatus for an internal combustion engine, which is applied to an internal combustion engine having a variable valve operating mechanism that makes a valve overlap state of an intake and exhaust valve variable and controls an internal EGR amount through a change in the valve overlap state,
A basic valve overlap area uniquely set from the engine speed and the engine load, and a basic internal EGR amount which is an internal EGR amount when the valve overlap area of the intake and exhaust valves is the basic valve overlap area, and Based on a target internal EGR amount that is a control target value of the internal EGR amount, a product of a ratio of the target internal EGR amount to the basic internal EGR amount and the basic valve overlap area is used as a control target of the valve overlap area. A control device for an internal combustion engine, wherein the control unit controls the internal EGR amount by controlling the variable valve mechanism as a value. A control apparatus for an internal combustion engine, which is applied to an internal combustion engine having a variable valve operating mechanism that makes a valve overlap state of an intake and exhaust valve variable and controls an internal EGR amount through a change in the valve overlap state,
A basic internal EGR amount, which is an internal EGR amount when the basic valve overlap amount uniquely set based on the engine speed and the engine load, and the valve overlap amount of the intake and exhaust valves is the basic valve overlap amount, and Based on a target internal EGR amount that is a control target value of the internal EGR amount, a multiplication value of a square root of a ratio of the target internal EGR amount to the basic internal EGR amount and the basic valve overlap amount is calculated as a value of the valve overlap amount. A control device for an internal combustion engine, wherein the control unit controls the variable valve mechanism as a control target value to control the internal EGR amount.

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